1. Field of the Invention
The present invention relates to a semiconductor device provided with a bump structure used for a flip-chip mounting.
2. Description of Related Art
In recent years, promoted energetically is realization of lead-free in design of the soldering for flip-chip mounting while taking into consideration of environmental problems.
As for lead-free solders, there is indicated the lead-free solder, which contains Sn, Ag and Cu. On the contrary, when forming a solder ball on a pad using such solders, in some cases, interfacial breakdown occurs between the pad and the solder ball.
Japanese Laid-Open Patent Publication No. 2001-93928 proposes technology to suppress such interfacial breakdown. According to the technology described in the Japanese Laid-Open Patent Publication No. 2001-93928, there is concluded that the intermetallic compound is the factor, which causes the interfacial breakdown of the solder ball to occur. From this viewpoint, the copper diffusion prevention film such as Ni, Cr or the like is formed on the copper pad so that the copper is prevented from reaching the surface of the solder ball while the copper being diffused. In such a way as above, this enhances reliability of the semiconductor device while preventing interfacial breakdown from occurring at the interface between the copper pad and the solder ball.
However, even the technology described in the Japanese Laid-Open Patent Publication No. 2001-93928, there is still room for further improvement on the point such as solder bump adhesion or the like. In addition, in the technology described in the same literature, it is necessary to form metal film such as Palladium film between the copper diffusion prevention film and the solder ball to ensure solder adhesion. However, in some cases, long term reliability of the pad portion cannot be obtained sufficiently.
In recent years, the case where the product is used under severe environment increases; and level of reliability required for the pad portion becomes higher.
In such a situation, new technology to suppress the interfacial breakdown and to improve reliability of the product is strongly required.